A capped ballpoint pen of the prior-art shown in FIG. 7 uses an ink which is endowed with a thixotropic property and which is poured directly into an ink-accommodating tube 1. The ink 2 that is endowed with a thixotropic property, such that the viscosity thereof is high in a static state but drops when the ball rotates during writing, is accommodated within the ink-accommodating tube. An ink follower 3 that follows the consumption of the ink and also prevents the ink from flowing backwards, is inserted at a rear portion of this ink. An engagement portion 9d of a tip holder member 9 is fitted in the front end of the ink-accommodating tube, and a ballpoint pen tip 4 is fitted in a front end aperture 9a thereof. A stopper 5 provided with a ventilation means is fitted in the rear end of the ink-accommodating tube 1. This type of ballpoint pen refill is inserted into a penholder tube B in a state such that only a writing portion protrudes from the front end thereof, and a front end portion of this penholder tube is covered by a cap C.
The prior-art ink-accommodating tube 1, shown in FIG. 8, has a smaller-diameter portion 1c that is open at the front end and a larger-diameter portion 1d that is open at the rear end. The ink 2 endowed with a thixotropic property and the ink follower 3 at the rear of this ink are incorporated within the ink-accommodating tube 1. The ballpoint pen tip 4 is fitted into a front end aperture 1a of the ink-accommodating tube 1, and a coil spring 7 that always presses a ball 6 against an inner reshaped surface 4f of a front end rim portion 4b that holds the ball is also disposed therein. The stopper 5 provided with a ventilation means (such as an opening) is fitted into the rear end of the ink-accommodating tube 1. This example relates to a refill which uses an ink having a thixotropic property and which is poured directly into an ink-accommodating tube, whereby drying of the ink at the front end of the tip or leakage thereof is prevented.
In the prior-art, a ballpoint pen or refill that uses a low-viscosity ink (a water-based ink) necessitates a complicated structure. This complicated structure may be similar to that of an internal-wadding type of water-based ballpoint pen wherein ink is guided to a tip end portion by a relay core in which ink is absorbed by an ink-absorbing member of cotton-like fibers covered by an outer film. Another example of a complicated structure may be that of a pen-core type of water-based ballpoint pen that uses a pen core member having an ink-flow adjustment function that comprises comb grooves which pour the ink directly into the ink-accommodating tube, ink grooves, and air grooves. A ballpoint pen or ballpoint pen refill which is formed by the direct pouring of an ink endowed with a thixotropic property, which provides clear handwriting with the same smooth writing feeling as that of a low-viscosity ink, has an advantage in that it is simple to pour the ink directly into the ink-accommodating tube. This feature is obtained because, although the ink maintains a high viscosity in a static state, the viscosity drops at the instant at which a shearing action occurs in the ink in contact with the ball surface when the ball rotates, so that the ink becomes a fluid.
On the other hand, if a state is assumed in which an impact force is exerted on the refill or ballpoint pen, the nature of the ink ensures that a shear action is generated at the contact surface between the ink and the ink-accommodating tube in the types of refill shown in FIGS. 7 and 8 as prior-art examples. The entire body of ink vibrates and thus the weight of the ink itself exerts an impact force on the ink follower when the tip is orientated upward or on the ball when the tip is orientated downward. An ink follower has certain physical properties such as viscosity and the degree of wetting thereof with respect to the inner surfaces of the ink-accommodating tube. However, all that supports the impact loading exerted on the ball is the force that holds the ball, which is produced by the process of reshaping the front end rim holding the ball. Consequently, if the impact force exceeds the force holding the ball, the ball could push the front end rim wider and fall out.
Therefore, of these ballpoint pens that use an ink endowed with a thixotropic property that is poured directly into an ink-accommodating tube, the type of pen that has a writing portion covered by a cap having a clip that can be attached to and removed from clothing (as shown in the prior-art example of FIG. 7) is carried in a state in which the tip is orientated upwards, so that there is no problem when this refill is used in a capped type of ballpoint pen. However, another application for this refill might be in a retractable type of ballpoint pen in which the tip is in a downward-orientated state and a pressing action on a pressing member accommodated within the holder tube causes a writing portion to protrude from or retract into an opening portion at a front end of the holder tube. In this case, there is a danger that an impact during the protrusion/retraction operation or while the pen is being carried could cause the ball to fall from the front end of the tip. If the ball falls out, ink will flow from the front end of the tip and stain the tube and clothing. Consequently, this refill has not been used in a retractable type of ballpoint pen up until now.
An objective of the present invention is therefore to provide a ballpoint pen refill that can be used without problems in a retractable type of ballpoint pen by using a configuration that completely prevents leakage or dripping from the front end of the tip, even when the tip is orientated downward. This refill also prevents the ball from falling out when it is subjected to an impact force and, if the ball should fall out for some reason, prevents the ink from flowing out from the front end of the tip.